Estimate lean body weight from adult height and weight with Boer, James, Hume and Janmahasatian equations. Compare each method, review estimated fat mass and lean percentage, or add a known body-fat percentage for a direct arithmetic estimate.
- Four published equations
- Metric and US units
- Formula-by-formula steps
- No data sent by the tool
Lean Body Weight Calculator
Enter adult measurements to compare four equations. Boer appears as the headline method, while the results table keeps every estimate separate and marks values that fall outside a plausible 0% to 100% of entered weight.
Male equation set at 180 cm and 80 kg
Boer composition estimate
76.8% leanThe bar is based on the Boer equation, not a scan or direct body-composition measurement.
Formula comparison
| Method | Lean weight | Lean % / fat mass | Substituted equation |
|---|---|---|---|
| Boer | 61.4 kg | 76.8% / 18.6 kg fat | 0.407 × 80 + 0.267 × 180 − 19.2 |
| James | 62.7 kg | 78.4% / 17.3 kg fat | 1.1 × 80 − 128 × (80 / 180)2 |
| Hume | 57.8 kg | 72.2% / 22.2 kg fat | 0.32810 × 80 + 0.33929 × 180 − 29.5336 |
| Janmahasatian | 61.7 kg | 77.2% / 18.3 kg fat | (9270 × 80) / (6680 + 216 × 24.6914) |
Calculation details
| Item | Result | Meaning |
|---|---|---|
| Entered measurements | 180 cm, 80 kg | Values used by all four equations |
| Calculated BMI | 24.69 kg/m2 | Used inside the Janmahasatian equation only |
| Plausible formula range | 57.8 to 62.7 kg | Lowest to highest estimate within 0% to 100% of entered weight |
| Formula spread | 4.9 kg | Difference between the plausible high and low estimates |
| Known body-fat method | Not entered | Add body-fat percentage to calculate weight × (1 − body-fat fraction) |
Calculation steps
- Use 80 kg for weight and 180 cm for height.
- Boer male estimate: 0.407 × 80 + 0.267 × 180 − 19.2 = 61.42 kg.
- Estimated Boer fat mass: 80 − 61.42 = 18.58 kg.
- Estimated Boer lean percentage: 61.42 ÷ 80 × 100 = 76.78%.
- The four plausible formula estimates span 57.79 to 62.72 kg and average 60.91 kg.
Recent calculations
Results stay in this page session. The calculator does not send your measurements.
How to Use This Lean Body Weight Calculator
- Select the male or female coefficient set published with the equations.
- Choose metric or US units. Enter adult height and current weight.
- If you already know an estimated body-fat percentage, enter it in the optional field. Leave it blank if you do not.
- Select “Calculate Lean Body Weight.”
- Review the Boer headline result, composition estimate, four-formula table and substituted calculation steps.
Enter feet and inches in separate fields. For example, use 5 feet and 10 inches rather than 5.10 or 5.8 feet. The tool converts US measurements to kilograms and centimetres before applying the equations, then converts displayed weight back to pounds when US units are selected.
What Is Lean Body Weight?
Lean body weight, often shortened to LBW, is total body weight minus fat mass. In everyday calculator language, lean body weight and lean body mass are often used for the same estimated quantity. It includes skeletal muscle, but it also includes bone, organs, connective tissue, body water and other non-fat components. A 60 kg lean-body estimate does not mean the person has 60 kg of muscle.
If body-fat percentage is already known, the direct arithmetic form is total weight multiplied by one minus the body-fat fraction. For 80 kg at 20% body fat, lean body weight is 80 × (1 − 0.20) = 64 kg. Fat mass is 16 kg. The quality of this answer depends on the quality of the body-fat estimate entered.
When body-fat percentage is unknown, equations estimate LBW from simpler measurements. This page compares four recognized adult equations instead of presenting one number as an exact measurement. Different equations use different source data and assumptions, so their results need not agree.
Lean Body Weight Formulas
In the equations below, W means weight in kilograms, H means height in centimetres and BMI means W divided by height in metres squared. Full precision is kept during calculation. Displayed values are rounded only at the end.
Boer formula
Female set: LBW = 0.252W + 0.473H − 48.3
Boer published the equation in 1984 while studying estimated lean mass as a way to normalize body-fluid volumes. This calculator uses Boer for the headline because it remains a widely recognized reference. It is still a prediction from height and weight, not a direct measurement.
James formula
Female set: LBW = 1.07W − 148(W / H)2
This implementation uses 128 in the male equation, matching the originally published James definition cited by the DICOM standards correction. Some older software used 120 after a secondary source error. The squared weight-to-height term also means James can turn downward at high weights and produce implausible results in severe obesity. The calculator displays the raw estimate but excludes a value outside 0% to 100% of entered weight from the “plausible” range and average.
Hume formula
Female set: LBW = 0.29569W + 0.41813H − 43.2933
Hume and colleagues published height-and-weight prediction equations in 1966. Like Boer, Hume is linear in height and weight. A linear formula is easy to audit, but it cannot represent every difference in age, build, hydration, illness, muscularity or fat distribution.
Janmahasatian formula
Female set: LBW = (9270W) / (8780 + 244BMI)
Janmahasatian and colleagues developed a semi-mechanistic equation in 2005 to predict fat-free mass across a wider body-size range. It uses BMI inside the denominator. This makes its mathematical behaviour different from the older linear equations and from the quadratic James formula. It is included for comparison, not as a universal replacement.
Worked Lean Body Weight Example
Consider an adult using the male equation set with weight 80 kg and height 180 cm. The Boer calculation is 0.407 × 80 + 0.267 × 180 − 19.2. The three parts are 32.56, 48.06 and 19.2, so estimated LBW is 61.42 kg.
Estimated fat mass from this equation is 80 − 61.42 = 18.58 kg. Estimated lean percentage is 61.42 ÷ 80 × 100 = 76.78%. The other results are about 62.72 kg with James, 57.79 kg with Hume and 61.73 kg with Janmahasatian. The plausible span is 57.79 to 62.72 kg, a spread of about 4.93 kg. Their simple average is about 60.91 kg.
Formula Comparison
| Method | Inputs | Useful feature | Important limitation |
|---|---|---|---|
| Boer, 1984 | Height, weight, coefficient set | Simple, transparent and widely cited | Prediction equation; source population may not represent every adult |
| James, 1976 | Height, weight, coefficient set | Recognized historical equation | Quadratic term can produce a paradoxical decline at high body weight |
| Hume, 1966 | Height, weight, coefficient set | Auditable linear relationship | Does not directly measure fat, muscle or hydration |
| Janmahasatian, 2005 | Height, weight, BMI, coefficient set | Developed across a broader body-size range | Still a population equation rather than an individual scan |
| Known body-fat method | Weight and body-fat percentage | Direct arithmetic from an existing body-fat estimate | Inherits error from the entered body-fat percentage |
Lean Body Weight Versus Related Measures
| Measure | What it represents | What it does not establish |
|---|---|---|
| Total body weight | All body mass shown by a scale | How much weight is fat, muscle, water or bone |
| Lean body weight | Total weight excluding estimated fat mass | Skeletal muscle alone or a diagnosis of health |
| Fat mass | Total weight minus estimated lean weight | Where fat is stored or its health effect |
| Body-fat percentage | Estimated fat mass divided by total weight | Exact composition when the measurement method has error |
| BMI | Weight relative to height squared | Direct separation of fat and lean tissue |
| Ideal body weight | A height-based reference from a separate equation | Actual lean body weight or one perfect target |
Why Calculator Results Differ
Each formula was built from different data and uses a different mathematical structure. Boer and Hume add linear contributions from weight and height. James subtracts a squared weight-to-height term. Janmahasatian uses BMI in a denominator. Even with identical inputs and correct arithmetic, these models produce different estimates.
Rounding and unit conversion also create small differences. This tool uses exactly 2.54 cm per inch and 0.45359237 kg per pound. It calculates in metric units at full precision and converts only for display. A site that rounds height or weight before applying a formula may show a slightly different answer.
The chosen coefficient set creates a larger difference. The source equations provide separate male and female coefficients, based on the body-composition data used by their authors. They do not include a separately validated nonbinary equation. A clinician can select an appropriate method when the purpose is clinical.
When an Estimate Is Not Plausible
Lean body weight should be greater than zero and no greater than total body weight. An equation can violate this basic range for unusual height-and-weight combinations or when used beyond the body sizes represented in its source data. The result then reflects a model limitation, not negative fat mass or more than 100% lean tissue.
This calculator does not silently clamp an equation to zero or to total weight. Clamping would hide the failed model. It shows the raw value, marks it as outside the plausible range, removes it from the summary range and average, and warns you. Consider a more suitable measurement or professional assessment instead of treating the flagged value as body composition.
Limits of Lean Body Weight Equations
They estimate rather than measure
Height-and-weight formulas cannot see muscle, bone, organ mass, fluid retention or fat distribution. Body-composition methods such as dual-energy X-ray absorptiometry, air-displacement plethysmography, isotope dilution, bioelectrical impedance and skinfold assessment use different measurements and assumptions. They can also disagree. A clinical team selects a method based on the question, equipment and patient context.
Hydration and illness matter
Lean mass contains water. Dehydration, edema, kidney or heart disease, inflammation, recent exercise, food intake and fluid shifts can change scale weight or affect body-composition methods. An equation from one height and one weight cannot explain the cause of a change.
Age and body proportions are missing
The four equations do not ask for age, ethnicity, limb proportions, amputation, spinal curvature, disability, pregnancy, menopause, training status or unusual muscularity. Older adults with low muscle mass and athletes with high muscle mass can have the same height and weight but different composition.
Children and pregnancy need separate assessment
Do not use this adult calculator for children or teenagers. Growth and body composition change with age and development. Do not use it during pregnancy to interpret pregnancy-related weight change. Seek age-specific or pregnancy-specific guidance from a qualified professional.
Can Lean Body Weight Guide Medication Dosing?
Some clinical protocols use lean, ideal, adjusted or actual body weight, but the correct size descriptor varies by medicine, procedure and patient. A public calculator does not know the drug, organ function, indication, route, laboratory results or protocol. Do not calculate or change a dose from this page.
The James coefficient issue shows why formula identity matters. Software implementations have differed between 120 and 128 in the male equation. Clinical work needs the exact method named in the responsible protocol and review by the prescriber or pharmacist. A formula estimate for general education is not a dosing instruction.
How to Improve Input Consistency
- Measure height without shoes on a firm, level floor.
- Use a reliable scale on a hard, flat surface.
- When tracking change, measure under similar conditions and at a similar time.
- Enter pounds and kilograms as weight, not force or stones without conversion.
- Keep feet and additional inches in separate fields.
- Do not guess a body-fat percentage to make an answer appear more precise.
- Check which formula and coefficient set another calculator uses before comparing results.
- Use a professional assessment when a medical decision depends on body composition.
Calculation Method and Review Sources
The Boer coefficients and study purpose were checked against the original record in PubMed. Hume’s height-and-weight prediction paper is available through PubMed Central. The Janmahasatian model and its fat-free-mass objective were checked against the Clinical Pharmacokinetics record.
The original 128 multiplier and the history of the 120-versus-128 James implementation difference were checked against the official DICOM correction document. The reported breakdown of the James formula in very high body weights was reviewed against a peer-reviewed PET imaging study. These sources support transparent equations and limits. They do not validate a personal diagnosis or treatment choice from this page.
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Frequently Asked Questions
What is the difference between lean body weight and lean body mass?
General calculators often use the terms for the same estimated non-fat body mass. It includes muscle, bone, organs, water and other non-fat tissue. Definitions and measurement models can differ in research or clinical protocols, so follow the exact definition required for that purpose.
Which lean body weight formula is most accurate?
No equation is most accurate for every adult and purpose. Boer, James, Hume and Janmahasatian use different source data and mathematical structures. Compare results and use an appropriate measured method when accuracy affects care.
Why do the four formulas give different answers?
Boer and Hume are linear equations, James includes a squared weight-to-height term, and Janmahasatian uses BMI in a denominator. Different source populations and coefficients lead to different estimates even when every calculation is correct.
Can estimated lean body weight exceed total weight?
A real lean component cannot exceed total body weight. A formula may do so for inputs outside its useful range. This calculator marks the raw value as implausible and excludes it from the plausible summary rather than hiding the model failure.
Why does the calculator ask for a male or female equation set?
The published formulas provide two coefficient sets. They do not publish a separately validated nonbinary set or account for hormones, transition history or individual composition. A clinician can choose a suitable method for a clinical purpose.
Why can the James formula fail at high body weight?
The James equation subtracts a term based on the square of weight divided by height. At sufficiently high weight, that subtraction grows faster than the first term, so the estimated lean mass can turn downward or become implausible.
How do I calculate lean body weight from body-fat percentage?
Multiply total weight by one minus body-fat percentage divided by 100. At 80 kg and 20% body fat, the calculation is 80 × (1 − 0.20) = 64 kg of estimated lean body weight.
Can I use this result for medication dosing?
No. The correct dosing weight and equation depend on the medicine, protocol, organ function and patient. Confirm every dose with the responsible prescriber or pharmacist rather than using this educational calculator.
Can children, teenagers or pregnant people use this calculator?
No. This page is designed for adult educational estimates. Children and teenagers require age-specific growth and body-composition assessment. Pregnancy needs pregnancy-specific weight guidance.
Does lean body weight mean muscle mass?
No. Skeletal muscle is one part of lean body weight. The estimate also includes bone, organs, water, connective tissue and other non-fat components.
Health and General Information Disclaimer
This calculator provides educational adult estimates only. It does not measure body composition, diagnose a condition, set a fitness or nutrition target, or provide medical, medication or financial advice. Do not use it for children, pregnancy or clinical dosing. Discuss health decisions and unexpected weight or body-composition changes with a qualified health professional.